Echocardiography has been going through major changes over the last few years: ultra-modern transducers and IT solutions have significantly improved 2D image quality while static and dynamic views offer entirely new insights into the heart.
Particularly in pediatric cardiology these improvements are highly welcome since ultrasound is and remains the diagnostic technology of choice for tiny hearts: no radiation, quick and flexible exams. “Excellent 2D image quality is the precondition for exact visualization of the anatomy – and thus for the evaluation of heart defects. However, the mere visualization of the heart has diagnostic limitations. In order to be able to evaluate
complex cardiac defects we also need to quantify ventricles and assess function,” says PD Dr. Kai Thorsten Laser, Deputy Director of the Pediatric Heart Center and Center for Congenital Heart Defects.
Until recently MRI was the only modality to reliably allow such functional analyses – but the technology is rather unsuitable for children since examination times of approximately 45 minutes require sedation or anesthesia. Consequently, the data pool with regard to MRI quantification is poor and there are no reliable reference values for ventricular volumes in the different age brackets.
PD Dr. Laser has for some time been exploring the possibilities with the develop a 3D analysis tool based on the TOMTEC software package to determine left and right ventricular volumes. “The software enabled me to measure volumes with comparable precision to the gold standard CMR. But we did not have any reference values for ultrasound measurements. Thus we conducted a multi-center study together with facilities in Bonn and Munich to evaluate children’s hearts.” In a first step the cardiologist and his team determined the overall suitability of the TOMTEC software package for measurement purposes: all pediatric patients who underwent diagnostic MRI also underwent a subsequent ultrasound exam. The results were assessed, blinded and compared to the MRI results. “The differences in the volume measurement results generated with ultrasound and MRI were minimal. 3D ultrasound yielded precise and valid results. And the results could be nicely reproduced and transferred to complex congenital heart defects with the interpretation workflow we had developed,” explains Kai Thorsten Laser. In a next step the team examined 360 healthy young hearts and used the results to establish reference values for different body sizes. “Currently the data pool for 3D ultrasound datasets is much larger than the one for MRI exams,” the pediatric cardiologist adds.
The software package PD Dr. Laser’s team used played a crucial role in the successful development of reference values that significantly facilitate the assessment of heart defects in pediatric patients. “In order to generate reproducible and valid results we have to stick to a certain workflow. This entails for the volume measurements of the right ventricle to control and possibly adapt the countours between blood and myocardium in many 2D sections taken from the 3D-dataset which improves the quantification results. Granted, today automatic contouration and evaluation work well. Nevertheless, when dealing with highly individual and complex issues such as pediatric heart defects they reach their limits. But together with TOMTEC we were able to overcome these obstacles. The TOMTEC team responded to our ideas and updated the software. Now we can view the entire data set and adapt contours as needed, even in the right ventricular outflow tract.”
At PD Dr. Laser’s Heart Center 3D echo is a standard component in the diagnostic work-up of left and right ventricular congenital heart defects, for example in patients with tetralogy of Fallot, a severe right ventricular defect. Children suffering from this condition have to be regularly examined after a first corrective operation since the pulmonary valve tends to leak. Volume measurements as well as calculation of ejection fraction play a major role in these exams. In the left ventricle, for example, enlarged chambers present in valvular heart disease can be reliably evaluated with ultrasound in order to determine valve dysfunction.
3D imaging, however, is not being used extensively since not many office-based cardiologists have access to the technology. Moreover the method, including workflows, requires careful training as PD Dr. Laser explains: “Now it will be our task to spread the method throughout the healthcare system, for example in workshops we will conduct jointly with TOMTEC. In these training sessions we have to explain why we think it is worthwhile to invest more time in the evaluation of 3D echos: it takes 5 to 10 minutes which is longer than the evaluation of 2D data. When you take into consideration that an MRI exam itself takes 45 minutes plus 20 minutes for the evaluation ultrasound offers a clear advantage in terms of time. Most importantly however: the children are spared the stress of sedation. This is major progress in diagnostics.”
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